1. Field of the Invention
The present invention relates to a method and apparatus for activating a hydrogen-absorbing alloy.
2. Description of the Related Art
A hydrogen-absorbing alloy is defined as a solid metal hydride (hereinafter, MH) capable of absorbing and desorbing hydrogen in the form of atoms in its crystal structure. Where a hydrogen-absorbing alloy is used for the storage of hydrogen, the hydrogen-absorbing alloy has to be activated before use by causing the hydrogen-absorbing alloy to absorb and release hydrogen repeatedly over several tens of cycles. When the hydrogen-absorbing alloy absorbs hydrogen, it expands and changes to reveal new surfaces, which promote changing the alloy into an active metal hydride.
Japanese Patent Publication No. 2000-17408 discloses one method for activating a hydrogen-absorbing alloy, in which an interior of a container (MH container) containing the hydrogen-absorbing alloy is held at a low pressure and a high temperature during release of hydrogen from the hydrogen-absorbing alloy. In contrast, during absorption of hydrogen by the hydrogen-absorbing alloy, the interior of the container is held at a high pressure and low temperature.
However, in the above conventional method, the hydrogen used for activating the hydrogen-absorbing alloy is not reused in a succeeding activation cycle. The hydrogen is supplied from an external hydrogen source to the MH container where the hydrogen is absorbed by the hydrogen-absorbing alloy in the container. However, after the hydrogen is released from the hydrogen-absorbing alloy, it is exhausted to atmosphere or is mixed with air to be burnt. As a result, to activate a hydrogen-absorbing alloy in an MH container of a volume of about 20 m3, hydrogen of a volume of about 200-1000 m3 is necessary. Further, since thermal energy is consumed independently in heating and cooling the interior of the MH container, the heat generated by the hydrogen-absorbing alloy during hydrogen absorption is not used to heat the hydrogen-absorbing alloy during hydrogen release.
An object of the present invention is to provide a method and apparatus for activating a hydrogen-absorbing alloy where an amount of hydrogen and an amount of thermal energy consumed during activation is greatly decreased.